This is a request for support of the above Gordon Research Conference to be held in New Hampshire, summer 1976. There is no forum which brings advances in the knowledge of the details of the fine structures and reactivities of the purines, pyrimidines and their derivatives together with the advances in detection and characterization of their myriad of biological activities and of related structure-activity and mechanism of action studies. Such derivatives are in clinical use in cancer chemotherapy and gout, and possibilities are not exhausted. Derivatives, some initially studied as cancer chemotherapeutics, have found roles in cardiovascular affects, platelet coagulation, and carcinogenesis. Others have roles in cell regulation and even in differentiation, in addition to their classical roles in most co-enzymes and in energy transfer. In the past decade tremendous strides in the understandings of the electronic structures and reactivities of these heterocycles promise that eventually the particular chemical and physical properties of purine and pyrimidine derivatives will be associated with their peculiar versatility in playing roles in such a variety of biological systems. This application also contains a unique proposal for future rescheduling after a longer time interval than is usual for Gordon Conferences.